This invention relates generally to a device for measuring the physical state of a work which is subjected to a high temperature atmosphere. More specifically, this invention relates to a device for measuring a change in the physical state of a work which is placed in a high temperature furnace by measuring the weight and dimension of the work.
As is well known, various objects or bodies of different materials, often referred to as works in the art, are treated or otherwise processed in a variety of high temperature furnaces. One example of such high temperature furnaces is a sintering furnace.
A typical work to be processed in the furnace is a body formed by powder metals or ceramics. The molded body or sample is made of a raw material mixed with wax and formed into a desired shape. The molded body is first dewaxed in the furnace and then subjected to a sintering process. Dewaxing is a process in which the molded body is heated in the furnace thereby to remove the wax contained in the molded body. If, in the course of the process, the temperature and pressure within the furnace are not controlled properly, the wax within the molded body vaporizes too quickly, or sintering proceeds at an unusually fast rate. This causes undesired cracks in and disfigurement of the molded body. In the past, however, it was next to impossible to perform a real-time measuring of any physical change that takes place within the work as it is processed in the furnace. In order to address these problems, it has been a common practice in the prior art to closely examine the works with cracks and fissures formed as they are taken out of the furnace in the midst of the sintering process, and adjust the temperature and pressure conditions in an effort to establish the optimum operation of the furnace for future processing which will eliminate or reduce to a minimum cracks and unwanted distortion in the molded bodies.
These conventional techniques for establishing the optimum operating conditions for the furnace have an inherent drawback that they largely depend on the skill and judgment of a seasoned operator and, therefore, lack objective criteria for selecting operating conditions, with a resulting poor yield of final products.
In the face of the problems, it has been attempted in recent years to install within a furnace various mechanisms for measuring the weight or dimension of a work to be treated in the furnace. With these measuring mechanisms, the weight of a sample body is determined by supporting it by the weight measuring mechanism, or else the vertical dimension of the sample body is measured by detecting by a sensing rod the distance between a position of the upper surface of the sample body and a position of a base on which the sample body is placed. However, the prior art arrangement is disadvantageous in that two separate measuring mechanisms must be provided at different locations, making the entire structure bulky and complex. Moreover, the weight and dimension measurement with the conventional arrangement is quite prone to error since the device has a pressure difference in the furnace, in order to prevent wax from staining the heat insulating material. This pressure difference causes error in weight measurement by changing the force on the supporting element of the work. Also, it causes error in dimension measurement by changing the contact force of the sensing rod which is placed on the work.